Currently, some agricultural and industrial equipment manufacturers design and construct vehicles which utilize load sensing systems. A load sensing system is one which varies the pump flow and fluid pressure to meet a load requirement and has one hydraulic function which has preference over other hydraulic functions. For example, the steering function of a vehicle may have priority over the hydraulic function which controls the movement of an attached implement. Besides steering, load sensing systems are useful on tractors and backhoe loaders where a single pump may be utilized to provide fluid to such devices as a brake unit, a differential lock or a hydraulic hitch as well as secondary circuits for other hydraulic devices such as actuators of selective control valves.
Some examples of load sensing systems are taught in U.S. Pat. Nos. 2,892,311, 4,034,563 and 4,116,001. These and other currently available systems are rather complicated in construction and costly because the power required by the primary circuit requires a variable flow rate at various pressures while still having priority over the secondary circuits. A further disadvantage of current load sensing systems, especially those used for steering, is that a kickback produced in the control valve is relayed through the steering wheel to the operator as pressure fluctuations occur within the system. Such kickbacks can become annoying to the operator and therefore there is a desire to essentially eliminate them.